Open-graded asphalt emulsion mixes

ABSTRACT

An open-graded emulsified asphalt paving mix is provided comprising a major portion of open-graded aggregate and a minor portion of cationic or anionic bituminous emulsion, the mix containing a minor portion of a polyelectrolyte having the opposite electric charge from that of the asphalt emulsifier which imparts excellent water resistance properties to pavement prepared from the mix. A method for producing the polyelectrolyte in situ is also provided.

RELATED APPLICATION

This is a division of application Ser. No. 178,056, filed Aug. 14, 1980,now U.S. Pat. No. 4,423,088 which is a continuation of Ser. No. 22,762filed 3/22/79, now abandoned, which a continuation-in-part of Ser. No.820,261 filed 8/1/77, now abandoned, which is a continuation-in-part ofSer. No. 732,849 filed 10/18/76, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to open-graded, emulsified asphalt pavements,compositions suitable for their preparation, and methods for theirpreparation.

Open-graded pavements are generally defined in the paving art asaggregate blends or asphalt mixtures which have high voids content. Thepavements may be prepared with either hot-mix asphalt or with asphalticemulsions. They possess the characteristics of relatively low cost, andthe ability to allow water drainage through the pavement structure. Thislast feature makes the pavements particularly desirable for overlays onexisting high-speed highways to prevent "hydroplaning" vehicle skidscaused by a film of water created between a smooth pavament surface andthe tire surface.

The open-graded, emulsified asphalt pavaments are of particular interestin remote areas far from plants where hot-mix asphalts are available.With the use of the emulsified asphalts, blending of the emulsions withthe aggregates may be performed in blending plants set up easily in theremote areas.

With the use of emulsified asphalts in constructing open-gradedpavements, several problems have, however, arisen. Because of the porousnature of the mix, the use of conventional slow setting emulsions (SStype) is not feasible. In such case, substantial amounts of the emulsionwill drain from the structure (runoff) before setting occurs, resultingin loss of asphalt. The onset of rain before complete set occurs willresult in the loss of even more asphalt from the pavement (washoff).Both runoff and washoff result in loss of strength in the pavement andpossible environmental contamination. Therefore, to reduce theseproblems, the emulsions used in these applications have been weaklystabilized medium setting (MS type) so designed that they "break" whenmixed with the aggregate. However, because of this early break,incomplete coating of the aggregate and poor adhesion of the asphalt andaggregate often occurs. In most cases, these results have beenameliorated by the addition of substantial quantities (5-15%, usually8-10%, by weight relative to the weight of emulsion) of petroleumnaphtha to the mixes. This results in softening of the asphalt providingbetter coverage and adhesion.

With the use of naphtha, new problems have arisen. First, the cost ishigh for the naphtha which is simply lost to the atmosphere byevaporation. Second, evaporation of the naphtha raises possible airpollution problems. Third, the hazard of fire during the operation isenhanced. Fourth, because naphtha softens the asphalt, the pavementrequires considerable time to achieve full strength, and the use ofheavy vehicles on the pavement before full strength is achieved mayresult in rutting of the surface. Therefore, it is desirable to produceopen-graded emulsified asphalt paving mixes which display good aggregatecoating properties and achieve desirable runoff and washoffcharacteristics without the use of naphtha, and form pavements whichdevelop their full strength rapidly.

2. Description of the Prior Art

Anionic polyelectrolytes such as the salts of synthetic polycarboxylicacids have been disclosed as primary emulsifiers and emulsionstabilizers, although not specifically for bitumens. Rohm and Haas Co.has described the use of neutralized acrylic polyacids marketed as"ACRYSOLS" as emulsifiers and as emulsion stabilizers with emulsionsproduced with nonionic emulsifiers.

Cationic polyelectrolytes, such as the quaternary salts of polyvinylpyridine have also been disclosed for use as emulsion stabilizers andemulsifiers (reference: "Cationic Quaternary Polyelectrolytes--ALiterature Review", M. Fred Hoover, a paper presented at the 159National ACS Meeting, Sept. 9, 1969).

SUMMARY OF THE INVENTION

A paving composition and the process for producing it. The pavingcomposition comprises about 80 to 97% by weight of an open-gradedaggregate and about 3 to 20% by weight of a cationic or anionicbituminous emulsion, said emulsion comprising about 40 to 75% by weightof asphalt, relative to the emulsion, about 0.25 to 5.0% by weightrelative to the emulsion of an emulsifier selected from the groupconsisting of cationic and anionic emulsifiers, and water as acontinuous phase of said emulsion to make up 100% by weight, saidcomposition also containing about 0.01 to 3.0% by weight relative to theemulsion of an ionic polyelectrolyte having an ionic charge opposite tothe selected emulsifier.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

We have now found that superior open-graded emulsified asphalt pavementcan be prepared from a novel mixture of open-graded aggregate, acationic or anionic (i.e., an ionic) emulsified asphalt, and a minoramount of an ionic polyelectrolyte which has the opposite charge to thatof the asphalt emulsifier. These mixes give excellent aggregate coating,provide pavements which rapidly reach maximum strength, possessexcellent water resistance properties (resistance to washoff and lowrunoff) without the presence of petroleum naphtha. Both cationicemulsified asphalt with a minor amount of an anionic polyelectrolyte andan anionic emulsified asphalt with a minor amount of a cationicpolyelectrolyte are contemplated.

In a preferred embodiment, an anionic polyelectrolyte will be producedin situ, i.e., by basification of the emulsion which will contain aminor portion of a polyelectrolyte precursor (PEP), a polymericpolyacid.

The application of these open-graded, emulsified asphalt mixes may becarried out in several ways, which are as follows:

(1) A polyelectrolyte may be added to the emulsion and the mixture maybe stored for a relatively short time, i.e., up to 4 hours. In somespecific cases, the mixture may be stored for as long as 100 hours. Theemulsion is then mixed with the aggregate shortly before application tothe road bed or road surface. This method, as well as all of the others,allows sufficient working time of the mix to allow working (screeding,etc.) of the mix before it hardens.

(2) The aggregate may be pretreated with the polyelectrolyte, and mixingof the emulsion with the aggregate takes place shortly beforeapplication of the mix.

(3) The aggregate, emulsion and polyelectrolyte may be mixed at one timeshortly before application.

Three additional methods may also be carried out with cationic emulsionsonly.

(4) A PEP may be used to pretreat the aggregate, and then the emulsion,in a form sufficiently basic to convert the PEP to the polyelectrolyteform, may be mixed with the aggregate.

(5) The aggregate, the PEP and the emulsion may be mixed together at onetime, and the mix basified by mixing in adequate base to neutralize theprecursor before use.

(6) A preferred method is to add the PEP to the emulsion, and mix theemulsion with the aggregate and base prior to use. The PEP-containingemulsion in this case may be stored for long periods.

One type of suitable asphalt emulsion is prepared with cationicemulsifiers. Among those are the emulsions described in U.S. Pat. Nos.3,026,266, 3,096,292, 3,220,953, and 3,445,258. Any suitable cationicemulsifier capable of emulsifying bitumen in water may be used includingcation active salts of quaternary nitrogen bases, salts of fatty amines,preferably straight-chain primary fatty mono and diamines, amidoaminesalts, such as amidoamine hydrochloride of stearic acid, etc., thehydrohalide salts of aminoamides of polyalkylene polyamines such astetraethylene pentamines and fatty acids, etc. Another class of suitableemulsifiers is that including the salts of ethylene oxide adducts offatty diamines and of the ethylene oxide adducts ofhydrocarbon-substituted imidazolines. This list is, of course, onlyillustrative, and not inclusive. The use of mixtures of the variouscationic emulsifiers is also contemplated. The preferred cationicemulsifiers are those described as the salts of quaternary nitrogenbases disclosed in U.S. Pat. No. 3,220,953. These compounds are thosematerials of the preferred formula ##STR1## in which R¹, R², R³ and R⁴are organic radicals, each having a carbon-nitrogen linkage to thenitrogen atom, X is an anion whose valence does not exceed 2, and m andn are small integers which indicate the molar proportions of the cationand anion required to form the respective salt. Preferred emulsifyingsalts are those in which the organic radicals R¹, R², R³ and R⁴ arealkyl, alkenyl, hydroxyalkyl, arylalkyl or alkylaryl radicals of 1 to 24carbons atoms or heterocyclic groups of 4 to 10 carbon atoms in whichfrom 2 to 3 of the nitrogen valences are shared by two carbon atoms in asingle heterocyclic group. In all of these salts of quaternary nitrogenbases suitable for use as cationic emulsifiers in the preparation ofoil-in-water type emulsions, the aggregate number of carbon atoms in thecationic portion of their molecule should be large enough to impart oilsolubility and emulsifying properties, and preferably should be equal toand not less than 15 and not more than 30 carbon atoms. In other words,this class of cationic quaternary nitrogen-containing compounds is formdby salts of tetra-substituted ammonium bases and by salts ofheterocyclic nitrogen bases, such as pyridinium, quinolinium,isoquinilinium, morpholininium, piperidinium, imidazolinium, and otherlike quaternary nitrogen-containing bases. The anion may be either ahalide (X⁻), a methosulfate (SO₄ CH₃ ⁻), a nitrate (NO₃ ⁻) or the likeion. Monovalent anions are preferred, particularly the halide anions.

Numerous cationic quaternary nitrogen-containing emulsifiers may beemployed for the preparation of cationic oil-in-water type emulsions.Among them, to mention but a few, are:

N,N-dimethyl-N-benzyl-N-octadecyl ammonium chloride,

N,N-dimethyl-N-hydroxyethyl-N-dodecyl ammonium chloride,

N,N-dimethyl-N-benzyl-N-octadecenyl ammonium chloride,

N,N-dimethyl-N-benzyl-N-dodecyl ammonium chloride,

N,N-dimethyl-N-hydroxyethyl-N-benzyl ammonium chloride,

Hexadecyl pyridinium chloride,

Hexadecyl triethyl ammonium bromide,

Octadecylbenzyl trimethyl ammonium methosulfate,

Isopropylnaphthyl trimethyl ammonium chloride,

Octadecyl pyridinium bromide,

1-(2-hydroxyethyl)-2-heptadecenyl-1-(4-chlorobutyl)imidazoliniumchloride,

Hexadecyl methyl piperidinium methosulfate,

Dodecyl hydroxyethyl morpholinium bromide.

Among the quaternary nitrogen-containing materials available in commerceas cationic emulsifiers for the preparation of oil-in-water typeemulsions, there are quaternary ammonium salts, such as quaternaryammonium halide materials sold by General Mills under the trademark"ALIQUAT"; materials sold by Armak Company under the several "ARQUAD"trademarks; certain quaternized materials developed and sold by theSociety of Chemical Industry, in Basel, Switzerland, under the several"SAPAMINE" trademarks, and many others.

The active cationic component of these materials contains thecharacteristic positively charged quaternary nitrogen configuration##STR2## in which the aggregate of carbon atoms of R¹, R², R³ and R⁴ issufficient to impart oil solubility and emulsifying properties, andpreferably is equal to not less than 15 and not more than 30 carbonatoms.

Best emulsification can be achieved with those among the aforesaidquaternary nitrogen-containing materials in which the active cationiccomponent contains at least one long aliphatic hydrocarbon chain of notless than 12 and not more than 24 carbon atoms, such as an alkyl or analkenyl chain. This latter chain may be derived from a mixture oforganic materials such as tallow, soybean oil, lard, etc.

The emulsifier material may consist entirely of an active cationic saltof a quaternary nitrogen base, or may also contain some impurities, suchas acyl chlorides and amines. It may also be employed in the form of aconcentrated aqueous solution and may contain auxiliary stabilizers inamounts conventionally employed in the trade.

Among the available commercial emulsifier materials of this type, thefollowing may be employed for the preparation of cationic emulsions inaccordance with the invention:

(1) HYAMINE 2389. This is the trademark of a product of Rohm and HaasChemical Company, of Philadelphia, Pa., for N-alkyl methylbenzyl-N,N,N-trimethyl ammonium chloride, which has the followingformula ##STR3## wherein R averages about 12 carbon atoms.

(2) ARQUAD T. This is the trademark of a product of Armak Company ofChicago, Ill., for C₁₄ -C₁₈ alkyl trimethyl ammonium chloride, which hasthe following formula: ##STR4## wherein R is a long alkyl chain derivedfrom tallow.

(3) HYAMINE 1622. This is the trademark of a product of Rohm and HaasChemical Company of Philadelphia, Pa., for di-isobutyl phenoxyethoxyethyl dimethyl benzyl ammonium chloride monohydrate of the formula

    [CH.sub.3.C(CH.sub.3).sub.2.CH.sub.2 (CH.sub.3).sub.2.C.sub.6 H.sub.5.OCH.sub.2 CH.sub.2.OCH.sub.2 CH.sub.2 N(CH.sub.3).sub.2.CH.sub.2 C.sub.6 H.sub.5 ].sup.+Cl.sup.-

(4) ARQUAD S. This is the trademark of a product of Armak Company ofChicago, Ill., for C₁₆ -C₁₈ alkyl trimethyl ammonium chloride, which hasthe formula: ##STR5## wherein R is a long alkyl chain derived fromsoybean oil.

It is believed that minor amounts of the starting materials ordinarilyare present in the aforementioned emulsifiers as impurities of noconsequence to their operativeness according to the invention.

These and other suitable cationic emulsifiers may be employed in varyingamounts, generally from about 0.25 to about 5%, and preferably fromabout 0.40 to about 2% of the active cationic component, based on theweight of the finished emulsion, although more or less may be employeddepending upon factors such as the cost of the emulsifier, itseffectiveness as an emulsifying agent, the amount of bitumen dispersed,etc. The asphalt will be present in the emulsion in the amount of fromabout 40 to 75, preferably 60 to 70, weight percent relative to theemulsion. The balance of the emulsion will be water to make 100%.

Another type of suitable asphalt emulsion is prepared with anionicemulsifiers. Among those are the emulsions described in Canadian Pat.No. 812,658, British Pat. Nos. 864,102; 1,149,257; and 1,165,517, andU.S. Pat. Nos. 2,730,506; 2,436,046; 2,855,319; and 2,512,580. Anysuitable anionic emulsifier capable of emulsifying bitumen in water maybe used, including the alkali metal salts of sulfonic acids andcarboxylic acids.

Carboxylic acid emulsifiers include the salts of fatty acids, naphthenicacids and cresylic acids. These salts are usually made from the alkalimetals, and sodium is the preferred metal. The carboxylic acid salts arepreferred.

Other carboxylic acid emulsifiers include the salts of tall oil acids,rosin acids, fatty acid pitch (residue from fatty acid distillation) andpine chip resin extract. This latter is the preferred carboxylic acidemulsifier.

The sulfonic acids used for forming anionic emulsions include thealkylaryl sulfonates having molecular weights in the range of 400 to500, e.g. Bis(dodecylphenyl)ether disulfonic acid, octadecylbenzenesulfonic acid, polypropylenebenzene sulfonic acid, dioctylbenzenesulfonic acid, etc. All of the above acids are utilized as their alkalimetal salts, preferably the sodium salt.

Naphthenic acids extracted from petroleum sources are good emulsifyingagents for this purpose. The acid number of such naphthenic acids shouldbe in the range of 75 to 175.

Polyelectrolytes are well-known substances (Encyclopedia of PolymerScience and Technology, Vol. 10, pages 781-854). Electrochemically apolyelectrolyte can be classified as polyacid, polybase orpolyampholyte. This application is principally concerned with thepolyacid and polybase polyelectrolytes. The polyelectrolyte additivesmay be described as water soluble high-molecular-weight polymers orcopolymers with ionized substituent groups along the backbone chain.These ionized groups may be anionic or cationic in nature. Suitablepolyelectrolyte precursors (PEP) are high-molecular-weight polymers orcopolymers with anionic ionizable groups along the chain. Theseionizable groups, namely acid groups, are readily converted to ionizedgroups by the addition of an appropriate base. These materials(polyelectrolytes and PEP's) may be either natural or synthetic.Preferably, the polymers used in this application are essentially linear(i.e. non-crosslinked); however, a small amount of crosslinking isacceptable provided that the polymer remains water soluble. Thepolyelectrolytes and the PEP's will usually be synthetic polymers havingaverage molecular weights (as measured by gel permeation chromatography)of at least about 1,000, preferably 10,000 and as high as 10,000,000.

The anionic substituent ionized groups will be the salts of acidicgroups attached to the polymer backbone, including for example,carboxylic acid groups, sulfonic acid groups, phosphonic acid groups,etc. Such acid groups are attached directly to the carbon atoms of thebackbone or attached through a connecting atom or atoms such as anoxygen or sulfur atom, an imino group, a polymethylene group orcombinations thereof. Examples of this type attachment includemonosulfate acid groups, monophosphate acid groups, methylene carboxylicacid groups, and the like. The preferred ionizable and ionizedsubstituents are the polycarboxylic acid and polycarboxylic acid salts.There will usually be from 2, preferably 3, to about 30 carbon atoms permonomer. That is, the polymer monomers will usually have from 3 to 30carbon atoms and 1 or more acidic groups.

Synthetic polymers and copolymers having ionizable or ionized groupsuseful for for this purpose are readily prepared by polymerizing orcopolymerizing the appropriate monomers. Preferably, the monomersconsist of monounsaturated compounds which undergo additionalpolymerization to form long, linear, polymers or copolymers. Theaddition of small amonts of di- or poly-unsaturated compounds willeffect a small amount of crosslinking. Non-crosslinked polyelectrolytesare preferred.

It is to be understood that the salt of the ionizable group and theionizable group itself may be formed after the polymer has been made as,for example, by hydrolyzing an anhydride such as polymaleic anhydride,or by saponifying a polyester, or polyamid, e.g., polymethacrylate, orpolyacrylamide; or by hydrolyzing a nitrile group, e.g.,polyacrylonitrile, etc.

Suitable acid or potential acid containing monomers for producing homo-or copolymers for this use include acrylic acid, acrylamide,acrylonitrile methyl acrylate, maleic anhydride, maleic acid,methacrylic acid, crotonic acid, allyloxyacetic acid, ethyl vinylacetate, itaconic acid, citraconic anhydride, dimethyl fumarate,furfurylacrylic acid, 5-norbornene-2-acrylic acid, N-phenylmaleamicacid, vinyladipic acid, p-styrene sulfonic acid, p-styrene sulfinicacid, ethylene sulfonic acid, allyl hydrogen sulfate, allyl dihydrogenphosphate, allyl methyl hydrogen phosphate, p-vinyl phosphonic acid, andthe like.

Suitable non-acid containing monomers useful for copolymerizing with oneor more acid-containing monomers as, for example, from the above list toform suitable polyelectrolytes include methyl vinyl ether, methyl vinylketone, allyl ether, acrylonitrile, vinyl acetate, allyl methylorthophthalate, vinyl octyl sulfide, ethylene, propylene, styrene,p-methoxy styrene, and others.

In addition, polymers with acid sulfate or acid phosphate ionizablegroups may also be prepared by sulfating or phosphating polyvinylalcohol with sulfuric or phosphoric acid.

Natural anionic polyelectrolytes useful for this process includehydrolyzed yeast or gum arabic, lignin sulfonates, polymerized rosinacids, etc. Protein polyelectrolytes including blood, casein, gelatinand the like are also suitable.

The preferred anionic polyelectrolytes are polyacrylic acid salts.

Suitable cationic substituent ionized groups are amino groups and thesalts of quaternized amino groups attached to the polymer backbone. Uponsolution in water, amines ionize by forming ammonium compounds withwater. The substituents are attached directly to the polymer backbone orthey may be attached through a connecting group such as a polymethylenegroup, a carbonyl containing group, an ether containing group, and arylgroup, and the like. Quaternary amino substituents are made by addingsufficient organic halide or sulfate containing molecules to primary,secondary or tertiary amino groups to convert most of the nitrogens tothe four-valent state, such that each nitrogen atom has four groupsdirectly attached to it and also has a net positive charge. Preferably,the quaternizing agents is methyl chloride.

Amino containing polymers may be prepared by homo- or copolymerizingunsaturated amino compounds. Among such compounds are vinylamine,ethylene imine, 4-vinylpyridine, 3-allylpyridine, N-allylpiperidine,allyl diethylamine, N,N-diethylaminoethylacrylamide,N,N-dimethylaminoethylmethacryic acid, vinylenedipyridine,2-vinylguanidine, p-diethylaminoethoxyethylmethacrylate, etc.

Amine-containing polymers may also be prepared by aminomethylation, asfor example by reacting polyacrylamide with formaldehyde anddimethylamine.

Suitable non-amine monomers useful for copolymerizing with one or moreamine-containing compounds to produce amine-containing copolymersinclude methyl vinyl ether, methyl vinyl ketone, allyl ethyl ether,acrylonitrile, vinyl acetate, allyl methyl ortho phthlate, ethylene,propylene, styrene, p-methoxystyrene, etc.

The polyelectrolytes will be employed in the mixes in a concentrationeffective to prevent runoff, usually from about 0.01 to 3.0%, preferably0.05 to 1.0%, by weight relative to the weight of the asphalt emulsion.

In a preferred embodiment, the additive will be an anionicpolyelectrolyte precursor when the emulsion is formed with a cationicemulsifier. This precursor will be a polymer corresponding to thepolyelectrolytes, but containing unneutralized acid groups. Thesematerials usually are sold in the form of aqueous emulsions. An exampleof such a material is Primafloc A-10, sold by Rohm and Haas Co.,Philadelphia, Pa. This material is described as an acid-containingpolyacrylic acid emulsion polymer. It and other related products havebeen described as beig useful as emulsion stabilizers in combinationwith non-ionic surfactants (primary emulsifiers).

The asphalt emulsions are prepared in the manner conventional foranionic or cationic bituminous emulsions. Thus, for example, inpreparing the cationic emulsions, the cationic emulsifier is firstdissolved in water, preferably at a temperature of 100°-125° F. Then theasphalt, heated at 240°-280° F. is dispersed in the resulting aqueoussolution in a colloid mill. Usually, from 60 to 70 parts of asphalt arethus emulsified with 30 to 40 parts of the water solution containing thecationic emulsifier and optionally other additives. The emulsion may beused immediately thereafter or, alternatively, stored for use at a latertime. The anionic emulsions are prepared in the same way using ananionic emulsifier.

In a preferred embodiment, the anionic polyelectrolyte precursor isadded in an appropriate amount to the emulsifying water prior topreparation of the cationic emulsion. In this form, the emulsion may bestored for extended periods of time prior to use; it will remain stablefor up to several months. Thus, at the application time, usually asufficient quantity of base is added to the emulsion to provide a pH tothe emulsion of greater than 7 and usually greater than about 11. Incertain cases, sufficient basicity is contributed by the aggregate toeffect neutralization of the polyelectrolyte without additional basebeing used. These cases usually occur with limestone-containingaggregates. Any base is suitable. Thus, suitable bases include a varietyof organic and inorganic bases. The alkali metal bases are preferred.Sodium hydroxide is particularly preferred.

Suitable aggregates for use with the emulsions of this invention includea wide variety of siliceous and calcareous materials. As previouslymentioned, the so-called "open graded" aggregates are preferred.

The open-graded asphalt mixes are described in "Design and Constructionof Emulsified Asphalt Open Graded Mixes and Overlays" by L. D. Coynepresented at the Twenty-Third Annual Road Builders Clinic, University ofIdaho, Moscow, Idaho, Mar. 17, 1972. Such a mix is generally defined asan aggregate blend or asphalt mixture which has a high voids content,usually lacking in fine aggregates (sand) and mineral fillers. FederalHighway Administration, Region 10, Emory Richardson, W. A. Liddle,"Experience in the Pacific Northwest with Open Graded Emulsified AsphaltPavements" defines the open-graded asphalt-paving mixes characterized bythe use of asphalt emulsion, aggregates as crushed stone or crushedgravel aggregate with less than 10 percent passing the No. 10 sieve and20 to 30 percent air voids in the compacted pavement. A consistentaspect of almost all definitions of open-graded aggregate is that lessthan 2 percent passes a No. 200 screen. The aggregate should preferablybe relatively clean, that is, the presence of substantial quantities ofdust will require higher quantities of emulsifier in the mixes. Thepaving composition will contain about 3 to 20, preferably 5 to 10,percent by weight of emulsion and about 97 to 80, preferably about 95 to90 percent by weight of open-graded aggregate based on the weight ofsaid paving composition.

EXAMPLES

The following examples illustrate this invention. The examples are onlyillustrative and are nonlimiting.

A specially-developed test was employed for evaluating the coatingability and water resistance of emulsions used in making open-gradedaggregate mixes. The test is a variation of ASTM Test Method D-244. Thetest specifically measures (1) coating, (2) stripping resistance, (3)runoff, (4) washoff, and (5) workability (stiffness) of the mixes. Thetest procedure is as follows:

(1) 100 g of open-graded aggregate is added to a mixing bowl.

(2) The aggregate is wetted with water which may contain base orpolyelectrolyte.

(3) The required amount (7 g.) of emulsion is added to the aggregate.

(4) The mixture is stirred for 15 seconds with a Hobart Mixer (using a"B" blade).

(5) Note is taken whether the emulsion disperses completely over theaggregate, and whether stripping occurs (asphalt being pulled fromcoated rock).

(6) The mixture is transferred to a pan with an aperture on one side.

(7) The pan is tilted and the quantity of emulsion that drains from theaperture is collected. Drying the drained material gives the asphaltlost by runoff.

(8) A portion of the mix is removed, and the ease of working isestimated. This sample is washed with cold water until the wash waterruns clear.

(9) The percent of asphalt coating is estimated for the washed andunwashed portions, the difference giving "washoff".

EXAMPLE 1

This example demonstrates the use of anionic polyeletrolytes incombination with a cationic asphalt emulsion. The emulsion was preparedfrom a 70/80 penetration paving grade asphalt at 65 weight percentrelative to the total weight of the emulsion. The emulsifier used wasArquad T-50, a cationic quaternary previously described, employed at aconcentration of 1% by weight relative to the emulsion.

The polyelectrolytes being tested were added as aqueous solutions to theaggregate before mixing with the emulsions. The total weight of waterand polyelectrolyte was 2% by weight relative to the aggregate. Thepolyelectrolytes used were:

(a) NaOH-neutralized Primafloc-A-10 (previously described);

(b) Dow Chemical Purifloc-A-23, a neutralized hydrolyzed polyacrylamide;

(c) Swift Chemical Co. Flocculant X-400.

The following Table I shows the results of the tests. The aggregatesemployed were a variety of types; in each 90% passed a 3/8 screen and isretained on a No. 4 screen and 10% passes a No. 10 screen and isretained on a No. 20 screen, except the dusty limestone which was agross-graded limestone containing about 2% dust passing a 200 screen.

                                      TABLE I                                     __________________________________________________________________________    Effect of Anionic Polyelectrolyte Pretreatment of Aggregate                   and a Cationic Asphalt Emulsion                                               Poly-                                                                         electrolyte       Workability*                                                                            % Coating @ 60 min.                                                                        Runoff,                              Test                                                                             Type                                                                              % wt.**                                                                            Aggregate                                                                           Initial                                                                           @ 60 min.                                                                           Before wash                                                                          After wash                                                                          wt. %                                __________________________________________________________________________    1  None                                                                              0    Granite                                                                             RM  RM    100    60    7.6                                  2  None                                                                              0    Silica                                                                              RM  RM    100    10    9.8                                  3  (b) 0.002                                                                              Granite                                                                             RM  RM    100    85    0                                    4  (b) 0.002                                                                              Silica                                                                              RM  RM    100    30    5.5                                  5  (c) 0.002                                                                              Granite                                                                             RM  RM     98    20    0                                    6  (c) 0.002                                                                              Silica                                                                              RM  RM    100    90    0                                    7  (a) 0.002                                                                              Granite                                                                             RM  RM    100    95    0                                    8  (a) 0.002                                                                              Silica                                                                              RM  RM    100    40    0                                    9  (b) 0.004                                                                              Granite                                                                             RM  RM    100    98    0                                    10 (b) 0.004                                                                              Silica                                                                              RM  RM    100    80    0                                    11 (c) 0.004                                                                              Granite                                                                             RM  RM     80    80    0                                    12 (c) 0.004                                                                              Silica                                                                              RM  RM    100    100   0                                    13 (a) 0.004                                                                              Granite                                                                             RM  RM    100    100   0                                    14 (a) 0.004                                                                              Silica                                                                              RM  RM    100    95    0                                    15 None                                                                              0    Gravel                                                                              RM  MS    100    50    14.3                                 16 None                                                                              0    Dolomite                                                                            RM  RM    100    10    27.1                                 17 None                                                                              0    Limestone                                                                           RM  RM    100    20    7.4                                  18 None                                                                              0    "Dusty"                                                                             RM  RM     98    90                                                     limestone                                                         19 (a) 0.004                                                                              Gravel                                                                              RM  RM    100    98    0                                    20 (a) 0.004                                                                              Dolomite                                                                            RM  RM    100    95    0                                    21 (a) 0.004                                                                              Limestone                                                                           RM  RM    100    100   0                                    22 (a) 0.004                                                                              "Dusty"                                                                             RM  RM/MS  95    95    0                                                limestone                                                         23 (a) 0.004                                                                              Granite                                                                             RM  RM    100    100   0                                    24 (a) 0.004                                                                              Silica                                                                              RM  RM    100    98    0                                    __________________________________________________________________________     *RM = readily mixable                                                         MS = moderately stiff                                                         **Relative to weight of aggregate                                        

These data show that effective coating and workability are attained, therunoff of the emulsions is eliminated, and washoff reduced by use of thepolyelectrolytes in pretreatment of the aggregates.

EXAMPLE 2

In this example, an anionic PEP was used in combination with a cationicasphalt emulsion.

In the following tests, the emulsion was prepared as in Example 1; tothat was added Primafloc A-10 (unneutralized), described above, at 0.3%by weight. The aggregate was prewet with 2% by weight of NaOH solutions(at different pH) relative to the weight of aggregate. Seven weightpercent of the emulsion was employed. The results of the tests are shownin Table II.

                  TABLE II                                                        ______________________________________                                        Effect of pH of Prewet                                                                             % Coating                                                                     @ 60 min.                                                             Workability.sup.1                                                                              After   Run                                              Prewet    Ini-   After  Ini- Wash  off,                              Aggregate                                                                              2% water  tial   60 min.                                                                              tial off   %                                 ______________________________________                                        1. Silica                                                                              pH 11.5.sup.2                                                                           RM     RM     100  30    7.6                               2. Silica                                                                              pH 12.0.sup.2                                                                           RM     MS     100  98    0                                 3. Silica                                                                              pH 11.5.sup.3                                                                           RM     RM     100  20    9.8                               4. Silica                                                                              pH 12.0.sup.3                                                                           RM     RM     100  100   0                                 5. Limestone                                                                           pH 11.5   RM     MS      98  85    0                                 6. Limestone                                                                           Dist. H.sub.2 O                                                                         RM     RM/MS   98  85    0                                 ______________________________________                                         .sup.1 RM = readily mixable                                                   MS = moderately stiff                                                         .sup.2 Stored at room temperature.                                            .sup.3 Stored at 140° F.                                          

These data show the activation of the polyelectrolyte precursor by basicsolution, the activation being enhanced with the more basic solution.Tests 5 and 6 show that effective activation occurs with certainaggregates with lower pH solutions. Storage at elevated temperatures,such as 140° F., does not destroy the effectiveness of the method.

EXAMPLE 3

Tests were performed with open-graded silica aggregate, varying theconcentration of the cationic emulsifier (Arquad T-50), thepolyelectrolyte precursor (Primafloc A-10), and the pH of the prewettingliquid. The polyelectrolyte precursor was added to the water along withthe cationic emulsifier prior to making the emulsion. The asphalt wasthe same type as that employed in Examples 1 and 2. The results are setforth in Table III, following.

                                      TABLE III                                   __________________________________________________________________________    Performance of Emulsion Prepared with Anionic Polyelectrolyte                 Precursor in Emulsifying Water of Cationic Asphalt Emulsion                                               % Coating                                         %     %                     @ 60 min.                                         Cationic                                                                            Polyelec-                                                                          Workability* After   After                                         Emulsifier                                                                          trolyte                                                                            Prewet (pH)                                                                            Initial                                                                           60 min.                                                                           Initial                                                                           Washoff                                                                            Runoff, %                                __________________________________________________________________________     1. 1 --   Dist. H.sub.2 O (5.7)                                                                  Loose                                                                             Loose                                                                             100 10   30.5                                      2. 1 0.3  "        "   "   100 20   4.8                                       3. 1 0.4  "        "   "   100 20   4.5                                       4. 1 0.5  "        "   "   100 30   5.0                                       5. 1.2                                                                             --   "        "   "   100 10   28.1                                      6. 1.2                                                                             0.3  "        "   "    80 30   0                                         7. 1.2                                                                             0.4  "        "   "   100 30   5.0                                       8. 1.2                                                                             0.5  "        "   "    60 30   0                                         9. 1.5                                                                             --   "        "   "   100 10   20.2                                     10. 1.5                                                                             0.3  "        "   "   100 10   11.9                                     11. 1.5                                                                             0.4  "        "   "   100 10   33.3                                     12. 1.5                                                                             0.5  "        "   "   100 10   23.1                                      1. 1 --   NaOH sol. (11.5)                                                                       "   "   100 10   33.8                                      2. 1 0.3  "        RM  RM  100 95   0                                         3. 1 0.4  "        RM  RM  100 98   0                                         4. 1 0.5  "        RM  RM  100 98   0                                         5. 1.2                                                                             --   "        Loose                                                                             Loose                                                                             100 10   29.5                                      6. 1.2                                                                             0.3  "        RM  Loose                                                                              80 40   0                                         7. 1.2                                                                             0.4  "        RM  RM  100 95   0                                         8. 1.2                                                                             0.5  "        RM  RM  100 98   0                                         9. 1.5                                                                             --   "        Loose                                                                             Loose                                                                             100 10   27.9                                     10. 1.5                                                                             0.3  "        RM  RM  100 40   0                                        11. 1.5                                                                             0.4  "        RM  RM  100 80   0                                        12. 1.5                                                                             0.5  "        RM  RM  100 90   0                                        __________________________________________________________________________     *RM = readily mixable                                                    

These data show that the emulsions prepared with the PEP present in theemulsifying water, when contacted with aggregate prewet with pH 11.5prewetting liquid, eliminate runoff and improve water resistance of thecoatings. Note that setting occurs with pH 11.5 prewet liquid in thiscase, whereas with the emulsions of Example 2, in which the PEP wasadded to the emulsion after its preparation, pH 11.5 liquid failed tocause setting, and pH 12 liquid was required.

EXAMPLE 4

In this test a cationic polyelectrolyte was used in combination with ananionic asphalt emulsion. The emulsion was prepared as in Example 1,except that 0.3% Vinsol Resin (Hercules Inc.) in dilute sodium hydroxidesolution was used as the emulsifier. The test procedure used was thatdescribed hereinabove before these examples.

Blends were prepared using the above anionic emulsion to which was addedPurifloc C-31 (Dow Chemical Co.), a cationic polyelectrolyte. PuriflocC-31 is a high-molecular-weight, water-soluble synthetic cationicpolyelectrolyte having the following approximate structure: ##STR6##Results are set forth in Table IV, following.

                  TABLE IV                                                        ______________________________________                                        Effect of Addition of Cationic                                                Polyelectrolyte to Anionic Asphalt Emulsion                                                        % Coating at                                                         Workability                                                                            60 min.                                                  Purifloc                  at 60                                                                              Before                                                                              After Runoff                             C-31, wt %                                                                            Aggregate Initial min. wash  wash  wt %                               ______________________________________                                        0       silica    Too     RM   100.sup.1                                                                           10    15.0                                                 loose                                                       0.1     silica    Too     RM   100.sup.1                                                                           20    3.0                                                  loose                                                       0.25    silica    RM      RM   100.sup.                                                                            90    0                                  ______________________________________                                         .sup.1 Thin coating.                                                     

These data show that without the polyelectrolyte, the emulsion wasreadily washed off the stones and had high runoff. With thepolyelectrolyte the water resistance of the mix was greatly improved,and runoff was eliminated.

EXAMPLE 5

Numberous other available anionic and cationic polyelectrolytes weretested with asphalt emulsions having the opposite charge. The method oftesting was the same as previously described and the following Table Vindicates the nature of the emulsion and the nature of the commercialpolyelectrolyte as well as the results obtained. Although the detailedchemical composition of the polyelectrolytes are not identified by themanufacturers, the results below illustrate the beneficial resultsobtained when an ionic polyelectrolyte is added to an asphalt emulsionof the opposite charge.

Miscellaneous cationic polyelectrolytes were evaluated in combinationwith an anionic emulsion made with 0.3% Vinsol Resin emulsifier by theprocedure of Example 1. The aggregate employed was an open-graded silicaaggregate. The data are given in Table V.

                                      TABLE V                                     __________________________________________________________________________    Evaluation of Miscellaneous Cationic Polyelectrolytes                         Product                        Polyelectrolyte                                                                          Runoff                              Identification                                                                       Supplier                                                                              Basic Composition per Supplier                                                                Concentration, wt %*                                                                     % (wt.)                             __________________________________________________________________________    None    --      --             --         21.8                                Gafaid Q                                                                             GAF     Quaternary Polyelectrolyte                                                                    0.1        0                                   Betz 1150                                                                            Betz    Cationic Acrylamide Copolymer,                                                                0.1        0                                                  MW 5,000,000                                                   Betz 1160                                                                            Betz    Cationic Acrylamide Copolymer,                                                                0.04       0                                                  MW 5,000,000                                                   Cato 8 National Starch                                                                       Cationic Corn Starch                                                                          1.98       0                                                  Derivatives                                                    Natron 86                                                                            National Starch                                                                       Cationic Polyelectrolyte                                                                      0.4        0                                   Primafloc C-7                                                                        Rohm and Haas                                                                         Cationic        0.06       0                                   Primafloc C-7                                                                        Rohm and Haas                                                                         Cationic        0.006      11.0                                Primafloc C-7                                                                        Rohm and Haas                                                                         Cationic        0.02       8.6                                 Primafloc C-7                                                                        Rohm and Haas                                                                         Cationic        0.04       0                                   Lufax 295                                                                            Rohm and Haas                                                                         Salt of Complex Polyamine                                                                     0.05       0                                   Catfloc                                                                              Calgon  Cationic Polyelectrolyte                                                                      0.25       0                                   Superfloc 16                                                                         American                                                                               --             0.20       0                                          Cyanamid                                                               Aqua-Rid                                                                             Reichhold                                                                              --             0.30       0                                   49-101                                                                        __________________________________________________________________________     *Relative to weight of emulsion                                          

Miscellaneous anionic polyelectrolytes were evaluated in combinationwith a cationic asphalt emulsion made with 1.0% Arquad T-50 emulsifier,by determining the minimum concentration of polyelectrolyte necessary toprevent runoff from open-graded Watsonville granite aggregate whentested by the procedures previously described. The data are given inTable VI.

                                      TABLE VI                                    __________________________________________________________________________    Evaluation of Miscellaneous Anionic Polyelectrolytes                                                             Minimum Concentration                      Product                            To Prevent Runoff                          Identification                                                                         Supplier Basic Composition per Supplier                                                                 (ppm)*                                     __________________________________________________________________________    Primafloc A-10                                                                         Rohm and Haas                                                                          Polyacrylic acid 5                                          #0627    Polyscience, Inc.                                                                      Polyacrylic acid, MW = 50,000                                                                  20                                         #4550    Polyscience, Inc.                                                                      Polyacrylic acid, MW = 100,000                                                                 20                                         #4551    Polyscience, Inc.                                                                      Polyacrylic acid, MW = 300,000                                                                 10                                         #6500    Polyscience, Inc.                                                                      Polyacrylic acid, MW = 1,000,000                                                               200                                        #6501    Polyscience, Inc.                                                                      Polyacrylic acid, MW = 4,000,000                                                               200                                        #3312    Polyscience, Inc.                                                                      Polyacrylic acid, MW = 250,000                                                                 100                                        #4652    Polyscience, Inc.                                                                      Poly (acrylamide-acrylic acid),                                                                20                                                           MW = 200,000                                                #0029    Polyscience, Inc.                                                                      Agar             >400                                       #2806    Polyscience, Inc.                                                                      Polyacrylamide, MW = 5 - 6 × 10.sup.0                                                    40                                         Resin 87D                                                                              Dow      Slightly anionic, low MW                                                                       100                                        Separan NP-10                                                                          Dow      Slightly anionic, medium MW                                                                    20                                         Separan PG-6                                                                           Dow      Anionic, low MW  20                                         Separan AP-30                                                                          Dow      Anionic, medium MW                                                                             20                                         Separan AP-273                                                                         Dow      Anionic, very high MW                                                                          20                                         Versa-TL 127                                                                           National Starch                                                                        Sulfonated Polystyrene,                                                                        400                                                          MW = 120,000                                                Daxad 15 W. R. Grace                                                                            Poly(alkylnaphthalene) sulfonic                                                                40                                                           acid                                                        Daxad 21 W. R. Grace                                                                            Poly aryl sulfonic acid                                                                        40                                         Magnifloc 834A                                                                         American Carboxylic salt  20                                                  Cyanamid                                                             Magnifloc 905N                                                                         American Carboxylic salt  40                                                  Cyanamid                                                             Magnifloc 870A                                                                         American Carboxylic salt  200                                                 Cyanamid                                                             Gantrez AN 119                                                                         Gen. Aniline                                                                           Poly(methylvinylether/maleic                                                                   100                                                 Film     anhydride)                                                  Gantrez AN 169                                                                         Gen. Aniline                                                                           Poly(methylvinylether/maleic                                                                   40                                                  Film     anhydride)                                                  PA-18    Gulf     Copolymer of octadecene-1 and                                                                  >400                                                         maleic anhydride, MW = low                                  T. P. Flocculant                                                                       Swift    --               20                                         X400                                                                          Nalcolyte 677                                                                          Nalco Chem.                                                                            Medium anionic   40                                         Jaguar 806                                                                             Stein Hall                                                                             Guar gum derivative                                                                            200                                        Jaguar CMHP                                                                            Stein Hall                                                                             Carboxymethylhydroxypropyl guar                                                                40                                         Gum Arabic                                                                             Stein Hall                                                                             Salt of Arabic acid                                                                            200                                        __________________________________________________________________________     *Relative to Emulsion                                                    

As will be evident to those skilled in the art, various modifications onthis invention can be made or followed, in the light of the foregoingdisclosure and discussion, without departing from the spirit or scope ofthe disclosure or from the scope of the following claims.

What is claimed is:
 1. A paving composition comprising about 80 to 97%by weight of an open-graded aggregate and about 3 to 20% by weight of acationic bituminous emulsion, said emulsion comprising about 40 to 75%by weight of asphalt, relative to the emulsion, 0.25 to 5.0% by weightrelative to the emulsion of a cationic emulsifier, and water as acontinuous phase of said emulsion to make up 100% by weight, saidcomposition also containing about 0.01 to 3.0% by weight relative to theemulsion of an ionic polyelectrolyte having an ionic charge opposite tothe emulsifier and comprising a salt of a polycarboxylic acid with anaverage molecular weight of from 1,000 to 10,000,000.
 2. The compositionof claim 1 wherein the cationic emulsifier is a salt of a quaternarynitrogen base.
 3. The composition of claim 2 wherein the cationicemulsifier is a C₁₄ -C₁₈ alkyl trimethyl ammonium chloride.
 4. Thecomposition of claim 1 in which the polyelectrolyte is a syntheticpolymer produced from monomers having from 3 to 30 carbon atoms.
 5. Thecomposition of claim 1 wherein the polyelectrolyte is a salt of apolyacrylic acid.
 6. The composition of claim 1 wherein thepolyelectrolyte is produced in situ by neutralization of apolyelectrolyte precursor.
 7. The composition of claim 6 wherein thepolyelectrolyte precursor is a polyacrylic acid.
 8. The composition ofclaim 1 wherein said polycarboxylic acid has a molecular weight of fromabout 1000 to about 10,000 and is a polymer of monomers containing from3 to 30 carbon atoms.
 9. A process for producing the composition ofclaim 1 wherein the polyelectrolyte is added to the emulsion.
 10. Aprocess for producing the composition of claim 1 wherein the aggregate,the emulsion and the polyelectrolyte are mixed simultaneously.
 11. Aprocess for producing the composition of claim 1 wherein apolyelectrolyte precursor is added with the emulsifier to the water usedto emulsify the asphalt, and the emulsion is combined with theaggregate, said aggregate containing sufficient base to neutralize saidpolyelectrolyte precursor promoting the setting of the paving mixture.12. An ionically charged bituminous emulsion comprising from 40% to 75%by weight of asphalt, from 0.25 to 5.0% by weight of an ionicallycharged emulsifier, from 0.01 to 3.0% by weight of a syntheticpolyelectrolyte precursor capable of being ionized into apolyelectrolyte having an ionic charge opposite to the ionic charge ofsaid emulsifier, and water as a continuous phase to make up 100% byweight wherein the polyelectrolyte precursor is a salt of apolycarboxylic acid having a molecular weight of from 1,000 to10,000,000.
 13. The emulsion of claim 12 wherein said polyelectrolyteprecursor is a polycarboxylic acid having a molecular weight of fromabout 1,000 to about 10,000 and is a polymer of monomer containing from3 to 30 carbon atoms.
 14. The emulsion of claim 12 wherein saidpolyelectrolyte precursor is a polyacrylic acid.